Photo-electric tube



Jan. 12, 1932. H. E. IVES PHOTO ELECTRIC TUBE Original Filed Aug. 20.

0 20 40 60' 30 ANGLE 0F INCIDENCE //7 van/0r: Herbs/2 T/ves m. A #yPatented Jan. 12, 1932:

UNITED STATES PATENT OFFICE HERBERT E. 1m, MONTCLAIB, JERSEY, ASBIGNOB'10 WESTERN ELECTRIC COMPANY, INCORPORATED, 0] NEW YORK, N. Y ACORPORATION 01 NEW YORK PHOTO-ELECTRIC TUBE Application filed August.20, 1925, Serial No. 51,308. Renewed June 9, 1931.

This invention relates to iinprovements in electro-optical apparatusand-particularly to photo-electric cells.

An object of the invention is to provide a light sensitive cell which ishighly eflicent in the generation of photo-electric currents.

The invention relates to photoelectric cells of the type in which theincident light is effective not only at the place on the cathode whereit is incident but at one or more other ode is a coating upon areflecting1 surface, referably a metallic surface who may be ighlypolished, the cathode coatin of light sensitive material being so thin tat light passes therethrough without appreciable absorption. Theinvention also rovides a cell structure in which substantia y all of theso light reaches the cathode at a h1 h angle of incidence and is manytimes re ected from one portion of the cathode to another.

Referring to the drawings, Fig. 1 shows a photo-electric cellrepresenting one embodiment of the invention.

Fig. 2 isa cross-sectional showing of the cell re resented in Fig. 1,the cross-section bein ta on along the line 22'.

igure 3 is a modification of Figs. 1 and 2 of iral cross-section.

showin the cathode in the form of connect ed ara lel plates. ig. 5illustrates a cell with the cathode in the form of convergent plates.

Fig. 6 shows curves giving the relation between the angles of incidenceof the light rays and the resulting hoto-electric current.

, It has been found at the alkali metals when placed in a well evacuatedchamber quickl cover with an extremely thin coating al points of thechamber with a photosensitive layer. This coating process is known asspontaneous deposition.

In a preferred embodiment of the invention the light sensitive cathodeis coated spontaneously with a thin film of an alkali metal such assodium, potassium, rubidium,

or caesium. Of these metals caesium has places to which the light isreflected. The. invention provides a cell in which the cath anode 11 arepermanently sealed in the arbor and shows the cathode in the form of aplate been found to trio eflect.

Referring to Fig. 1 there is shown one form of construction for carryingout the invention. The cell shown in Fig. 1 comprises an evacuated glassvessel 1, into which are sealed the electrodes 8 and 11. As shown thecell consists of a cylindrical bulb with'a comparatively long neck ofsmaller diameter. The drawn out portion of the cell is reentrant toprovide the usual sealing-in portions 2 and 3 through which theconductors 4 and 5 pass. Sealed in the portions 2 and 3 arethe-electrode supporting wires 6 and 7. The supporting wire 7 alsoserves as a conducting means to the cylindrical cathode 8. For thepurpose of main give the greatest photo-electaming the supporting andconducting wires equally spaced and to provide a comparatively rigidstructure, an arbor 9 of glass or other suitable insulating material isprovided. W es 6 and 7 which support and make contact with the cathode 8as well as wire 10 which supports and contacts with the central 9. Otherforms of mounting and contacting with the electrodes such as arewell-known in the art may be employed without departing from the purposeand spirit of the invention.

As shown in Fig. 1 the cathode 8 consists of a metal plate turned intothe form of an incomplete cylinder. The opening 12 between the edges ofthe cathode is for the purpose of allowing the light beams to impingeupon the interior light sensitive surface of the cathode. The cathodemay be of any material, but is preferably metallic. It has been foundfrom experiment that a platinum plate which is capacable of retaining ahigh polish provides a very eflicient base for the coating of the lightsensitive substance.

The preferred method of spontaneously coating the cathode 8 with a .thinfilm of a light sensitive substance, such as caesium, is that describedin the Astro-Physical Journal, Volume LX No. 4,'November 1924. It is tobe noted that the spontaneous deposition of the alkali metal appears tohave no effect on the color or surface character of the underlyingplate. Accordingly when a highly substance does not affect this polish.Ad-

Astrovantage is taken of this fact to provide multiple reflection of thelight rays as Wlll appear hereinafter. The thickness of the coatin maybe regulated as described in the Thysical Journal, Volume LX No. 4,November, 1924.

The anode 11 may consist of any suitable metal preferably tungsten. Fig.1 shows the anode in the form of a 'rod but it is to be understood thatother forms may be emloyed such as, for example, a cylindrical orm or aflat plate form.

Fig. 2 shows a cross-section of the elements of the cell illustrated inFig. 1 and discloses the manner in which the cell is employed inconjunction with an optical s stem to produce the enhancedphoto-electric effect. This figure shows a source of light 13 which,'bymeans of an appropriate optical system represented by the lens 14,causes the rays of li ht 15 to enter the opening 12 between the erfgesof the cylindrical cathode 8 in such a manner as to be incident upon thecathode surface at a very high angle. As a result of thus causing therays to impinge at a high angle of incldence and because of thecylindrica'l shape of the cathode, a greater photoelectric current isproduced than has heretofore been possible. For a given intensity oflight from the source 13 this result is a direct function of the angleof incidence of the light rays.

Fig. 6shows themanner in which the photo electric efl'ect varies withthe angle of incidence. This figure is the same as Fig. 5 of the articleappearing in the Astro-Physical Journal referred to hereinbefore. Inthis fi re the abscissae represent various angles 0 incidence of thelight rays upon the light sensitive surface, while the ordinatesrepresent the corresponding currents for a given potential impressedupon the anode of a photoelectric cell employing a thin film of lightsensitive material deposited upon a polished surface. Curve A shows theangle versus current relation when the light sensitive substance is inthe form of a thin, spontaneously de osited film on a polished platinumplate. gurve B shows this relation when the light sensitive substanceforms a solid layer. It will be observed from these curves thereforethat the photo-electric effect obtainable from extremely thin layers ismuch greater than the effect obtained from comparatively thick layers.It will also be observed that the photo-electric current increasesrapidly with the angle of incidence until a maximum is reached the rateof increase being very large for thin films.

From a consideration of these curves, therefore, it is seen that toproduce the greatest photo-electric efiect in a given cell fora '85, themaximum current being obtained at an'angle of incidence of approximately7 5- Wh1le light directed upon a light sensitive surface at a high angleof incidence produces a large photoelectric current, a still furtherincrease is realized when employing in addition a light sensitivesurface adapted for multiply reflecting the light incident thereon. Thusby utilizing a photo-electric cell such as shown in Fig. 1 with a thinspontaneously depositing coating of alkali material, such as caesium, ona highly polished platinum plate together with means for allowing thelight rays to be incident at the appropriate angle, the maximum eflfectis produced. As may be gathered from an inspection of Fig. 2 because ofthe highly polished character of the inner surface of cathode 8, andbecause of its cylindrical structure, each ray is multiply reflectedon'the light sensitive surface at a high angle.

Fig. 3 shows a modification of Figs. 1 and 2 with a plate cathode ofspiral cross-section. The cathode 16 may be of any suitable metalcapable of retaining a high polish and oi being cleaned-by electronbombardment as is well-known in the art. The light sensitive film may beof caesium, rubidium, or other alkali metal. It will be noted in thearrangement of Fig. 3 that for a given cathode area a greater reflectingpower is retained, thus proportionately increasing the photo-electri(eflect.

Fig. 4 shows another modification in whicl the cathode consists of2parallel plates 17 and 18 electrically connected by the conductoi 19.Instead of a central anode in the forn of a wire rod such as shown inFigs. 1, 2 and 3, an anode in the form of an incom plete cylinder 20 isemployed. The lighi from source 21 enters through the opening 23 and isfocused by means oflens 22 upor the plates 17 and 18 at the optimumangle 0: incidence. Because, of the parallel arrange ment of the cathodeplates, the angle of inci dence and reflection is constant. If desire(the wire 19 may be replaced by a flat plati of the same material asplates 17 and 18 anr covered with the same light sensitive sub stance,thus providing further reflecting power for the light rays reflectedupon th plates 17 and 18.

Fig. 5 shows a still further modification o: the electrodes. 11 thiscase an incompleti cylind cal anod 25 is used similar to tha reflectionsobtaina 1e with such an arrange.

ment.

From the foregoing description it will be seen therefore that applicanthas produced a photo-electric cell in which advantage is taken of theincreased photo-electric effect produced by the multiple reflectingpower of the cathode plates together with means for causing the lightrays to be incident upon these plates at a very steep angle.

What is claimed is:

1. A photoelectric cell comprising an anode, and a cathode comprising ahighly polished surface thinly coated with a transparent lightelectrical active film which surface specularly reflects light incidentthereon, the photoelectric effect being at a maximum when the lightwhich actuates the cell is incident upon the electrode surface withinthe range of angles of incidence between 40 and 85.

2. A photoelectric cell comprising an anode, and a cathode comprising asurface coated with a transparent light electrical active film, thephotoelectric effect being at a maximum when the light which actuatesthe cell is incident upon the cathode surface within the range of anglesof incidence between 40 and 85.

3. A photoelectric cell comprising an anode, and a cathode comprising asurface coated with a transparent light electrical active film, thephotoelectric effect being at a maximum when the light which actuatesthe cell is incident upon the cathode surface at an angle of incidenceof the order of 75.

4. A photoelectric cell comprising an anode, and a cathode comprising ahighly polished surface coated with a transparent light electricalactive film, which surface multiply reflects light incident thereon, thephotoelectric effect being at a maximum when the light which actuatesthe cell is incident u on the cathode surface within the range angles ofincidence between and 85.

5. A photoelectric cell comprising an anode, and a cathode comprising asurface coated with a transparent li ht electrical active film, thephotoelectric e ect being at a maximum when the light which actuates thecell is incident upon the cathode surface within the range of angles ofincidence between 40 and 85, said cathode reflecting light incident ata. certain angle within said range upon one portion of the surfacethereof to another portion of said surface.

6. A photoelectric cell comprising an anode, and a cathode having aplurality of portions,

the light sensitive surfaces of which portions are opposite each other,whereby when the activating light is incident upon one of said surfacesat an angle of incidence within the range of from 40 to 85 the incidentlight will be reflected to the sensitive surface of the other of saidportions, the photoelectric effect being at a maximum when the incidentlight is within said range.

7. A photoelectric cell comprising an anode, and a cathode having aplurality of extended plane portions, the light sensitive surfaces ofwhich ortions are opposite each other whereby wiien the activating lightis incident upon one of said surfaces at an angle of incidence withinthe range of from 40 to 85 the incident light will be reflected to thesensitive surface of the other of said portions, the photoelectriceffect being at a maximum when the incident light is within said range.

In witness whereof, I hereunto subscribe my name this 17th day ofAugust, A. D., 1925.

HERBERT E. IVES.

